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Abstract
Background:
Pneumonia is a common illness in all parts of the world and is considered as a major cause of death among all age groups. Nevertheless, only about 5% of patients referring to their primary care physicians with acute respiratory symptoms will develop pneumonia.Objectives:
This study was performed to derive practical criteria for performing chest radiographs for the evaluation of community-acquired pneumonia (CAP).Patients and Methods:
A total of 420 patients with acute respiratory symptoms and positive findings on chest radiograph were evaluated from December 2008 to December 2009. The subjects were referred to outpatient clinics or emergency departments of Birjand's medical university hospitals, Iran, and were enrolled as positive cases. A checklist was completed for each patient including their demographic information, clinical signs and symptoms (cough, sputum production, dyspnea, chest pain, fever, tachycardia, and tachypnea), abnormal findings in pulmonary auscultation and laboratory findings (erythrocyte sedimentation rate, C-reactive protein levels, and white blood cell count). An equal number of age-matched individuals with acute respiratory symptoms, but insignificant findings on chest radiography, were included as the control group. Finally, the diagnostic values of different findings were compared.Results:
The data showed that vital signs and physical examination findings are useful screening parameters for predicting chest radiograph findings in outpatient settings. Therefore, by implementing a prediction rule, we would be able to determine which patients would benefit from a chest X-Ray (sensitivity, 94% and specificity, 57%).Conclusion:
This study's findings suggest that requesting chest radiographs might not be necessary in patients with acute respiratory symptoms unless the vital signs and/or physical examination findings are abnormal. Considering the 94% sensitivity of this rule for predicting CAP, a chest radiograph is required for patients with unreliable follow-ups or moderate to high likelihood of morbidity if CAP is not initially detected.Keywords
Pneumonia Mass Chest X-Ray Prediction Rule Acute Chest Syndrome
1. Background
Pneumonia is a common illness all around the world and is considered as a major cause of death among all age groups (1). In Iran, pneumonia is the most common cause of hospitalization in the elderly and patients with primary antibody deficiencies (2, 3). Nonetheless, only 5% and 28% of patients with acute respiratory symptoms who are referred respectively to primary care physicians (4) and emergency departments (EDs) (5) develop pneumonia. According to most clinical guidelines, the gold standard tool for diagnosing pneumonia is a chest X-ray (CXR), which can distinguish this condition from other respiratory tract infections (6). However, many clinicians might only rely on the patient’s medical history and physical examination findings to diagnose or exclude pneumonia.
Community-acquired pneumonia (CAP) is the most common type of pneumonia. Despite frequent use of X-ray in clinical settings, there are still debates regarding its necessity in patients suspected of having CAP. In this regard, Ayalon et al. investigated the role of physical examination in the diagnosis of pneumonia and demonstrated the significant benefit of CXR as an ancillary test for the diagnosis of pneumonia in ED settings (7). In addition, according to a review published in 2003, CXR was considered as the gold standard for diagnosing pneumonia. Researchers doubted that the decision to perform CXR should solely rely on experts' opinions, which are based on strategies for optimizing the balance between harms and benefits. Consequently, they recommended a combination of the patient’s medical history, physical examination, and laboratory data to estimate short-term risks and to determine the appropriate treatment (8).
2. Objectives
Although several investigators have attempted to provide prediction rules to improve the detection of CAP in outpatient settings during the past three decades, there have been contradictory conclusions in this regard (4, 9-17). Accordingly, the aim of the present study was to evaluate the predictive value of the eight most common clinical parameters and three most frequent laboratory variables in patients presenting with acute respiratory symptoms. Therefore, the subjects were divided into two large groups of 420 to determine the effect of clinical and laboratory data for X-ray-based diagnosis. The groups were as follows: the case group included those with positive CXR findings and the control group consisted of subjects with insignificant CXR findings.
3. Patients and Methods
In this case-control study, all adult patients (18 years of age or older) with acute respiratory symptoms (one or more of the following symptoms: cough, sputum, dyspnea, and chest pain) and positive findings on CXR were included as positive cases (n = 420). The subjects had been referred to outpatient clinics or EDs of medical university hospitals in Birjand, Iran, from December 2008 to December 2009. Positive findings on CXR were defined as the presence of new consolidations without an air bronchogram, pleural effusion, abscess or empyema in the setting of acute respiratory symptoms. Patients with subtle airspace opacities (equivocal findings) were also considered as positive cases. An equal number of cases (n = 420) with acute respiratory symptoms but insignificant findings on CXR were recruited as the control group; the subjects were matched in terms of age and the date of the CXR procedure. Those with findings suggestive of hospital-acquired pneumonia (positive findings on CXR within ten days of discharge), aspiration pneumonia, and those who had recently received antibiotics or steroids were excluded.
An infectious disease specialist examined all patients and the data regarding clinical symptoms and signs were recorded. Afterwards, CXRs were performed and the clinician was blinded to the radiographic results. A board-certified radiologist, unaware of the clinical findings, interpreted all CXRs. The clinical indicators included cough, sputum production, dyspnea, chest pain, fever (body temperature≥ 38℃), tachycardia (heart rate≥ 100 beats per minute), tachypnea (respiratory rate≥ 20 breaths per minute), and abnormal findings on pulmonary auscultation and examination (crackles, decreased breath sounds, dullness on percussion, and rhonchi). The erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) levels, and white blood cell (WBC) count were measured for all patients. Abnormal values of these laboratory tests were defined as follows: ESR (mm/h) higher than the males’ age divided by two or females’ age plus ten divided by two (16), CRP > 5 mg/L (47.62 mmol/L), and WBC > 10000/µL or < 4000/µL.
The sensitivity and specificity of all clinical indicators were calculated using the IBM SPSS 19 software for Windows (IBM Corp., IBM SPSS Statistics for Windows, Armonk, NY: IBM Corp.); odds ratios (OR) were also calculated for each of the indicators. Additional indicators were defined as “any abnormal findings in vital sign assessment” (positive test results = fever, tachycardia, and/or tachypnea), “any abnormal findings in vital sign assessment or physical examination” (positive test results = fever, tachycardia, tachypnea, and/or abnormal findings on pulmonary examination) and “any abnormal findings in laboratory test” (positive test results = abnormal values of ESR, CRP, or WBC). According to the analyses, we attempted to provide a prediction rule to determine which patients would benefit from CXR. The diagnostic accuracy of this rule was determined regarding the area under the receiver operating characteristic (ROC) curve.
4. Results
During the 12-month study period, 420 patients with acute respiratory symptoms and positive findings on CXR were eligible for participating in the study. An equal number of individuals were selected as the control group with similar demographic characteristics as the case group (Table 1). The analyzed data are presented in Table 2. The clinical symptoms and signs were compared, and as listed in Table 2, there was a significant difference between the two groups regarding clinical indicators including fever, tachycardia and tachypnea (abnormal vital signs). Similarly, the difference between the two groups in terms of pulmonary auscultation according to physical examination was statistically significant. With regards to the aims of this study, the sensitivity and specificity (95% confidence interval) of the statistically significant variables were calculated (Table 2). The clinical indicator with the greatest sensitivity for pneumonia (diagnosed by CXR) was cough, with a sensitivity of 89.5%.
The presence of “any abnormal findings in vital sign assessment”, “any abnormal findings in vital sign assessment or physical examination”, and “any abnormal findings in laboratory test” was studied, and these indicators were compared according to the recorded data (Table 2). All three of these new “combined indicators” exhibited higher prevalence in patients with CAP (positive findings on CXR in the setting of acute respiratory symptoms) in comparison with the controls. However, only for one parameter (any abnormal findings in vital sign assessment or physical examination), the sensitivity (94.0%), specificity (57.4%), and OR (23.1) were optimal for being used as a screening parameter. This combined prediction rule had an area under the ROC of 0.751, which suggested that it was a relatively effective rule with 75% accuracy and 94% sensitivity. Table 2 lists the sensitivity and specificity of other clinical, laboratory, and “combined” indicators. Elevated CRP alone had a specificity of 94.6%. The sensitivity of elevated ESR was 28.3%, whereas its specificity was 86.9%.
| Variables | Case Group (No. = 420) | Control Group (No. = 420) |
|---|---|---|
| Mean Age, y | 60 | 63 |
| Age Range, y | 18-87 | 19-86 |
| Gender | ||
| Male | 220 (52.4) | 227 (54.0) |
| Female | 200 (47.6) | 193 (46.0) |
| Underlying Lung Disease c | 50 (11.9) | 28 (6.7) |
Analysis of Clinical and Laboratory Indicators in Patients with Acute Respiratory Symptoms a
| Indicators | Cases (n = 420) b | Controls (n = 420) b | Sensitivity c (95% CI) | Specificity c (95% CI) | Odds Ratio (95% CI) |
|---|---|---|---|---|---|
| Cough | 376 (89.5) | 272 (64.8) | 89.5 (86.7-91.5) | 35.5 (30.4-40.8) | 4.6 (2.9-6.7) |
| Sputum | 354 (84.3) | 168 (40.0) | 84.3 (80.6-87.0) | 60.0 (55.4-64.7) | 8.0 (5.6-10.4) |
| Dyspnea | 323 (76.9) | 180 (42.9) | 76.9 (72.6-80.4) | 57.1 (60.5-70.2) | 4.4 (2.7-6.5) |
| Chest pain | 315 (75.0) | 201 (47.9) | 75.0 (71.1-79.0) | 52.1 (46.3-57.3) | 3.5 (2.4-5.1) |
| Fever d | 285 (67.9) | 68 (16.2) | 67.9 (62.9-73.2) | 83.8 (80.1-86.5) | 7.0 (4.8-10.2) |
| Tachycardia d | 231 (55.0) | 63 (15.0) | 55.0 (49.6-59.4) | 85.0 (81.0-88.4) | 6.9 (4.7-10.1) |
| Tachypnead | 252 (60.0) | 44 (10.5) | 60.0 (55.3-64.9) | 89.5 (86.5-91.5) | 12.8 (7.6-17.4) |
| Abnormal Auscultation Findings e | 370 (88.1) | 133 (31.7) | 88.1 (85.1-90.3) | 68.3 (63.3-73.6) | 16.0 (11.2-20.8) |
| Elevated ESR | 119 (28.3) | 55 (13.1) | 28.3 (22.3-33.6) | 86.9 (82.8-90.3) | 7.2 (5.1-10.3) |
| Elevated CRP | 168 (40.0) | 22 (5.2) | 40.0 (34.7-45.4) | 94.6 (91.8-96.7) | 12.7 (7.5-17.3) |
| Abnormal WBC | 204 (48.6) | 94 (22.4) | 48.6 (42.7-54.0) | 77.6 (73.4-81.1) | 3.3 (2.2-4.9) |
| Any Abnormal Findings in VS | 361 (86.0) | 118 (28.1) | 86.0 (81.9-89.4) | 77.9 (73.7 81.5) | 9.5 (7.2-12.8) |
| Any Abnormal Findings in VS or PE | 395 (94.0) | 179 (42.6) | 94.0 (91.1-96.3) | 57.4 (60.8-70.5) | 23.1 (12.7-43.1) |
| Any Abnormal Findings in LAB | 254 (60.5) | 110 (26.2) | 60.5 (55.2-65.5) | 73.8 (69.8-77.7) | 6.8 (4.5-10.0) |
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